1. Field of the Invention
The present invention relates to a novel disk drive. More specifically, the present invention relates to a technique which allows high-speed seek operations, a reduction in pickup movement errors, and size reduction.
2. Description of the Related Art
There have been conventionally used two types of mechanisms for moving a pickup which performs reading of information from and/or recording of information to a disk. They are the rack-and-pinion mechanism in which a rack gear of a pickup is moved forwardly by means of a pinion gear, and the lead screw mechanism in which a nut member of a pickup is moved forwardly by means of a lead screw.
In the rack-and-pinion mechanism, the rotation of the motor is slowed down and transmitted, through a plurality of reduction gears, to the pinion gear which engages the rack gear of the pickup.
This, however, causes the seek time of the pickup to be lengthened.
In addition, in the rack-and-pinion mechanism, a plurality of reduction gears are interposed between the motor and the pinion gear, so that the total backlash between the gears is increased, resulting in a larger error in movement of the pickup with respect to the number of rotations of the motor.
When an attempt is made to eliminate backlash, which causes errors in the movement of the pickup, between the gears, a mechanism for eliminating the backlash is required, so that more parts are required, the number of manhours required for assembly is increased, costs are increased, and the disk drive becomes larger.
In the lead screw mechanism, the amount of movement of the motor with respect to the number of rotations of the motor is small, so that, here again, the seek time is lengthened. In addition, the disk drive becomes thicker.
In a disk drive used for writing information to or reading recorded information from a disk, information is written or read by moving a pickup in a radial direction of the disk. In order to write and read information to and from the disk, it is necessary to accurately irradiate, for example, laser beams, emitted from the pickup, perpendicular to or at a specified angle from an information recording surface of the disk.
In such a disk drive, in order to allow the pickup to move freely from the inner periphery to the outer periphery of the disk, the pickup is guided using two guide shafts, and is moved as a result of transmitting driving power of a motor, or the like, to the pickup.
In conventional disk drives, the two guide shafts, used for guiding the pickup, as well as the spindle motor, used for rotating the turntable that holds and allows rotation of the disk, are mounted to the chassis.
For this reason, the degree of parallelism between the two guide shafts and the mounting portion of the stator base that supports the spindle motor is greatly affected by the degree of flatness and the dimensional precision of the chassis. When the degree of flatness or the dimensional precision of the chassis is reduced, the degree of parallelism between the guide shafts and the stator base is also reduced, causing, for example, laser beams from the pickup to strike the information recording surface of the disk obliquely rather than vertically (angle from the vertical will hereinafter be referred to as "skew angle"). When the skew angle becomes large, the performance of the disk drive is greatly reduced.
In order to maintain the performance capabilities of the disk drive, it is necessary to keep the skew angle close to zero by making the chassis as flat as possible and its dimensions as precise as possible. Therefore, it becomes difficult to produce the chassis, chassis yield and thus disk drive yield are reduced, thus making it difficult to produce disk drives in large quantities, and increasing costs.